Synergistic effect of Pd+Rh on the microstructure and oxidation resistance of aluminide coatings

Abstract

The Pd+Rh modified aluminide coating were deposited on nickel and CMSX-4 nickel superalloy. The Pd layer (2.5 ?m thick) with next Rh layer (0.5 ?m thick) were electroplated on both nickel and CMSX-4. The aluminizing of the substrates with Pd+Rh layers were performed by the CVD method. Two zones (outer and interdiffusion) were observed on both coatings. The palladium doped ?-NiAl phase formed in the outer zones and palladium and rhodium doped ?-NiAl phase was formed at the outer/interdiffusion zone border of both coatings. The ??-Ni3Al phase and ?-Co7Mo6 precipitates in the ?-NiAl matrix were found in the interdiffusion zone on nickel and CMSX-4 superalloy respectively. The simultaneous usage of Pd and Rh in the aluminide coating slowed their oxidation rate, moreover the Pd+Rh co-doping is more efficient than Pd+Hf in reducing the oxidation rate of aluminide coating on CMSX-4 superalloy.